1. Field of the invention
The present invention relates to a method for manufacturing a group III nitride compound semiconductor laser diode (hereinafter xe2x80x9cLDxe2x80x9d). In particular, the present invention relates to a method for manufacturing a facet of a cavity of an LD.
2. Description of the Related Art
A light-emitting diode (LED) and a laser diode (LD) which emit blue light have been known, which comprise layers of gallium nitride group compound semiconductor (AlGaInN) formed on a sapphire substrate. A verticality and a parallelism of one pair of opposite facets of a cavity should be kept high to reflect and oscillate lights of an LD effectively. Although a cleavage is the best way to form one pair of opposite facets which has high verticality and parallelism, it is difficult to cleave the facets of the LD because the substrate and the layers are made of different materials. Accordingly, dry etching is used to form the facets as an alternative method of the cleavage.
However, the facets of the cavity formed by dry etching is damaged by ion and has a magnitude of surface roughness of 200 xc3x85. As a result, an optical reflectiveness of the facets is lowered and the oscillation threshold current density is heightened. In case that reflection films are formed on the facets of the cavity, the films cannot be formed accurately as designed because the facets of the cavity are rough. As a result, lights are scattered on the facets and the efficiency of confining emitted lights in an active layer is lowered.
It is therefore an object of the present invention to improve a mirror reflection of the one pair of opposite facets of a cavity of the LD, to improve the efficiency of confining lights by improving the optical reflectiveness, and to lower an oscillation threshold current density.
The present invention is related to a method for manufacturing a laser diode using Group III nitride compound semiconductor comprising the steps of forming layers comprising Group III nitride compound semiconductor on a substrate, dry-etching each of said layers to form one pair of opposite facets of a cavity, and further etching said dry-etched facets by gas cluster ion beam etching. As a result, the surface roughness of the facets of the cavity by dry etching is reduced by gas cluster ion beam etching, a mirror reflection of the facets is improved, the effect of confining lights between the opposite facets is increased, and an oscillation threshold current density of the LD is lowered.
A Group III nitride compound semiconductor should be preferably a material satisfies the formula AlxGayIn1xe2x88x92xxe2x88x92yN(0xe2x89xa6xxe2x89xa61, 0xe2x89xa6yxe2x89xa61, 0xe2x89xa6x+yxe2x89xa61) to obtain blue color short wave LD. When the semiconductor is formed by a cladding layer of Gax1In1xe2x88x92x1N (0xe2x89xa6x1xe2x89xa61) and an active layer of Gax2In1xe2x88x92x2N(0xe2x89xa6x2xe2x89xa61), output power of the blue color LD is improved. The facets are effectively formed by reactive ion beam etching (RIBE hereinafter) more than by dry etching. It is more preferable to use RIBE with Cl2 gas, because a higher etching rate can be obtained. Further, a rough layer on the facets formed by dry etching is removed effectively by gas cluster ion beam etching, and a mirror reflection of the facets is improved. The mirror reflection of the facets is improved to form the facets by gas cluster ion beam etching using inert gases like argon (Ar), helium (He), neon (Ne), krypton (Kr), xenon (Xe), radon (Rn), nitrogen (N2), and carbon dioxide (CO2) or reactive gases like hydrogen chloride (HCl), chlorine (Cl2), carbon chloride trifluoride (CClF3), bromine (Br), and hydrogen bromide (HBr). Then a wafer treated by above-mentioned process is divided into peaces of strip parallel to the facets of the cavity. Each of the strips are disposed with the facets of the cavity facing upside, and the facet is etched by cluster beam etching to improve the efficiency of a mirror reflection of the facet.